Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
TYLENOL W/ CODEINE NO. 4 vs ACETAMINOPHEN AND PENTAZOCINE HYDROCHLORIDE
Clinician-reviewed, head-to-head comparison of mechanism, dosing, pharmacokinetics, and safety profiles.
Last clinically reviewed: July 2026 · OpiCalc Medical Review Team
Codeine is a prodrug that undergoes O-demethylation by CYP2D6 to morphine, which acts as a μ-opioid receptor agonist, inhibiting adenylate cyclase and modulating neurotransmitter release in the CNS. Acetaminophen inhibits cyclooxygenase (COX) enzymes, primarily in the CNS, reducing prostaglandin synthesis and modulating pain perception.
Pentazocine is a mixed agonist-antagonist opioid analgesic that binds to mu, kappa, and sigma opioid receptors, primarily acting as an agonist at kappa receptors and partial agonist at mu receptors, resulting in analgesic and sedative effects. Acetaminophen (paracetamol) is an analgesic and antipyretic whose mechanism involves inhibition of cyclooxygenase (COX) enzymes, primarily COX-2, in the central nervous system, and possibly activation of descending serotonergic pathways.
Management of mild to moderate pain where an opioid analgesic is needed
Moderate to severe pain where an opioid analgesic is appropriate
One or 2 tablets (acetaminophen 300 mg-codeine 60 mg per tablet) orally every 4 hours as needed for pain; maximum 12 tablets per day.
One tablet (acetaminophen 500 mg / pentazocine hydrochloride 25 mg) orally every 4 hours as needed for pain; maximum daily dose: acetaminophen 4000 mg (8 tablets) and pentazocine hydrochloride 200 mg (8 tablets).
Codeine: Terminal half-life of 2.5-3.5 hours; however, its active metabolite morphine has a half-life of 1.5-2 hours, and morphine-6-glucuronide (M6G) has a half-life of 2-4 hours. Acetaminophen: Terminal half-life of 2-3 hours in adults; prolonged in hepatic impairment (up to 4-5 hours) or overdose (4-12 hours). Clinically, duration of analgesic effect is approximately 4-6 hours.
Acetaminophen: 2-3 hours (prolonged in hepatic impairment). Pentazocine: 2-3 hours (terminal), with clinical analgesic effect lasting 3-4 hours.
Codeine: metabolized by CYP2D6 to morphine (active), CYP3A4 to norcodeine, and glucuronidation. Acetaminophen: extensively metabolized in the liver via conjugation (glucuronidation, sulfation) and minor oxidation by CYP2E1 to N-acetyl-p-benzoquinone imine (NAPQI), which is detoxified by glutathione.
Pentazocine is extensively metabolized in the liver via oxidation and glucuronidation; significant first-pass metabolism. Acetaminophen is metabolized primarily in the liver via conjugation with glucuronide and sulfate, and oxidation via CYP2E1, CYP1A2, and CYP3A4 to a toxic metabolite (NAPQI).
Codeine and its metabolites (including morphine, morphine-6-glucuronide, and norcodeine) are primarily excreted renally. Approximately 90% of a codeine dose is excreted in urine within 24 hours, with 5-15% as free codeine, 5-13% as free morphine, 40-60% as codeine conjugates, and 5-10% as morphine conjugates. Fecal excretion accounts for less than 5%. Acetaminophen is primarily metabolized in the liver to glucuronide and sulfate conjugates; about 85% of a dose is excreted renally as conjugates within 24 hours, with 2-4% excreted unchanged. Minor biliary/fecal elimination occurs for both drugs.
Acetaminophen: renal (2-4% unchanged, ~85% as glucuronide and sulfate conjugates). Pentazocine: renal (~60% as unchanged and conjugates), biliary/fecal (~20%).
Codeine: Approximately 20-40% bound to plasma proteins (primarily albumin). Morphine: 20-35% bound. Acetaminophen: 10-25% bound to albumin. Binding is minimal and generally not clinically significant.
Acetaminophen: 10-25% (albumin). Pentazocine: 60-70% (albumin and alpha-1 acid glycoprotein).
Codeine: Vd approximately 3-4 L/kg (range 2.5-5 L/kg). Acetaminophen: Vd approximately 0.9 L/kg (range 0.7-1.0 L/kg). Codeine's larger Vd indicates extensive tissue distribution; acetaminophen distributes evenly throughout body fluids.
Acetaminophen: 0.9 L/kg. Pentazocine: 5-7 L/kg (extensive tissue distribution).
Oral: Codeine bioavailability is approximately 50-60% (first-pass metabolism). Acetaminophen bioavailability is 70-90% (absorbed rapidly from GI tract; first-pass metabolism minimal). Rectal bioavailability of acetaminophen is approximately 80-90% of oral.
Acetaminophen oral: 60-90%. Pentazocine oral: ~20% (extensive first-pass metabolism). Intramuscular: pentazocine 100%.
e GFR 30-50 m L/min: use with caution, reduce dose by 25%. e GFR <30 m L/min: not recommended due to risk of accumulation and respiratory depression.
Cr Cl 30-50 m L/min: use with caution; decrease dose interval to every 6 hours if needed. Cr Cl <30 m L/min: restrict pentazocine; consider alternative. Not recommended for patients on dialysis.
Child-Pugh class A: caution, maximum 2 tablets per dose; class B or C: contraindicated.
Child-Pugh Class A: no adjustment. Child-Pugh Class B: reduce pentazocine dose by 50%; avoid acetaminophen >2 g/day. Child-Pugh Class C: contraindicated due to acetaminophen hepatotoxicity and pentazocine accumulation.
Not recommended for children under 12 years. For ages 12-18: weight-based codeine dosing 0.5-1 mg/kg/dose every 4-6 hours (max 60 mg/dose); acetaminophen 15 mg/kg/dose every 4-6 hours (max 75 mg/kg/day). Use lowest effective dose.
Not recommended in children <12 years due to lack of safety data. For adolescents ≥12 years, adult dosing may be considered based on weight (≥50 kg).
Initiate at half the adult dose (1 tablet) every 4 hours due to increased sensitivity to opioids and acetaminophen hepatotoxicity; maximum 8 tablets per day. Monitor renal and hepatic function closely.
Reduce pentazocine dose by 50% (e.g., one tablet every 6 hours) due to increased risk of CNS depression, confusion, and constipation. Monitor renal function; avoid exceeding 4 g/day acetaminophen.
WARNING: ADDICTION, ABUSE, AND MISUSE; LIFE-THREATENING RESPIRATORY DEPRESSION; ACCIDENTAL INGESTION; ULTRA-RAPID METABOLISM OF CODEINE AND OTHER RISK FACTORS FOR LIFE-THREATENING RESPIRATORY DEPRESSION IN CHILDREN; NEONATAL OPIOID WITHDRAWAL SYNDROME; HEPATOTOXICITY; INTERACTION WITH ALCOHOL; RISKS FROM CONCOMITANT USE WITH BENZODIAZEPINES OR OTHER CNS DEPRESSANTS; RISK OF MEDICATION ERRORS.
Pentazocine: Risk of respiratory depression, particularly in elderly, cachectic, or debilitated patients. Concomitant use with benzodiazepines or other CNS depressants may result in profound sedation, respiratory depression, coma, and death. Patients should be monitored for respiratory depression and sedation.
Risk of addiction, abuse, and misuse,Life-threatening respiratory depression, especially in patients with compromised respiratory function,Accidental ingestion of even one dose, especially by children, can be fatal,Ultra-rapid metabolism of codeine to morphine due to CYP2D6 polymorphism leading to toxicity,Neonatal opioid withdrawal syndrome with prolonged use during pregnancy,Hepatotoxicity due to acetaminophen, especially with doses >4000 mg/day or with concurrent alcohol use,Interaction with alcohol and other CNS depressants,Concomitant use with MAOIs or within 14 days is contraindicated,Avoid use in children <12 years of age and in children <18 years after tonsillectomy/adenoidectomy
Respiratory depression risk, especially in patients with compromised respiratory function,Potential for opioid dependence, abuse, and misuse,Risk of withdrawal if discontinued abruptly after prolonged use,Pentazocine may cause opioid withdrawal in patients dependent on pure mu agonists,Acetaminophen hepatotoxicity at high doses or with chronic use; risk increased with alcohol consumption or pre-existing liver disease,Central nervous system depression additive with other CNS depressants,Elderly or debilitated patients may have increased sensitivity to effects,May cause hypotension, especially in hypovolemic patients,Serotonin syndrome risk when used with serotonergic drugs,Pentazocine may cause hallucinations, confusion, or other psychotomimetic effects
Hypersensitivity to codeine, acetaminophen, or any component,Significant respiratory depression,Acute or severe bronchial asthma in an unmonitored setting or without resuscitative equipment,Known or suspected gastrointestinal obstruction, including paralytic ileus,Concurrent use of monoamine oxidase inhibitors (MAOIs) or within 14 days,Children <12 years of age,Children <18 years of age after tonsillectomy/adenoidectomy
Hypersensitivity to either component,Severe respiratory depression (e.g., acute asthma, hypercapnia),Acute or severe bronchial asthma,Suspected surgical abdomen (may obscure diagnosis),Monoamine oxidase inhibitor (MAOI) use (current or within 14 days),Severe hepatic impairment or active liver disease (acetaminophen component),Known or suspected gastrointestinal obstruction (including paralytic ileus)
Avoid alcohol and foods containing alcohol (e.g., desserts, sauces) due to increased risk of hepatotoxicity and CNS depression. No specific food restrictions otherwise.
Avoid alcohol consumption due to increased risk of hepatotoxicity from acetaminophen. No specific food interactions; take with food if gastrointestinal upset occurs.
Pregnancy Category C prior to 2015; current data insufficient for definitive risk. Acetaminophen: no consistent evidence of major malformations; codeine: opioid use in first trimester associated with small increased risk of neural tube defects (OR 1.1-1.3); third trimester use may cause neonatal opioid withdrawal syndrome (NOWS) and respiratory depression at delivery.
Acetaminophen: Generally considered low risk; no consistent evidence of teratogenicity in any trimester. Pentazocine: Limited human data; animal studies show no teratogenicity at clinically relevant doses. However, use in third trimester may cause neonatal respiratory depression and withdrawal syndrome. Overall, risk is low but pentazocine should be avoided near term.
Acetaminophen is compatible (low levels in milk). Codeine is present in milk; M/P ratio approximately 2:1 (morphine). Caution: ultra-rapid CYP2D6 metabolizers may produce high morphine levels leading to infant toxicity. Use lowest effective dose for shortest duration; monitor infant for drowsiness, difficulty breathing.
Acetaminophen: Excreted in low amounts (M/P ratio ~0.2-0.9); compatible with breastfeeding. Pentazocine: Excreted in breast milk; M/P ratio unknown; may cause CNS effects in infants. Use with caution, especially in neonates or premature infants. Monitor infant for sedation and respiratory depression.
No specific dose adjustment recommended for acetaminophen; codeine pharmacokinetics altered in pregnancy (increased clearance, decreased half-life). Avoid codeine in pregnancy if possible; if used, lowest effective dose for shortest duration. Consider alternative analgesics (e.g., acetaminophen alone). Postpartum: resume standard dosing.
Acetaminophen: No significant pharmacokinetic changes in pregnancy; standard dosing (max 3-4 g/day) applies. Pentazocine: Clearance may increase due to enhanced hepatic metabolism; dose adjustments not routinely recommended but monitor response. Avoid high doses near term due to risk of neonatal depression.
Each tablet contains acetaminophen 300 mg and codeine phosphate 60 mg. Maximum acetaminophen dose: 4 g/day; avoid other acetaminophen-containing products. Codeine is a prodrug; CYP2D6 poor metabolizers may have reduced efficacy, while ultra-rapid metabolizers risk toxicity. Monitor for respiratory depression, especially in opioid-naive patients. Use with caution in patients with liver impairment or G6PD deficiency.
Pentazocine is a mixed agonist-antagonist opioid; avoid in opioid-dependent patients due to risk of precipitated withdrawal. Acetaminophen component limits total daily dose to 4 g (or less in hepatic impairment) to prevent hepatotoxicity. Monitor for respiratory depression, especially in elderly or those with COPD. Injection site reactions (e.g., sterile abscesses, fibrosis) common with repeated intramuscular use. May cause dysphoria, hallucinations, or CNS stimulation (unlike typical opioids). Contraindicated in acute porphyria due to porphyrinogenic potential.
Do not exceed 12 tablets in 24 hours due to acetaminophen content.,Avoid alcohol while taking this medication.,This drug may cause drowsiness; do not drive or operate machinery until you know how it affects you.,Contact your doctor if you experience signs of allergic reaction (rash, difficulty breathing) or liver injury (yellowing of skin/eyes, dark urine).,Do not take with other products containing acetaminophen (e.g., Tylenol, cold medicines).,Codeine can be habit-forming; use only as prescribed.,Women who are breastfeeding should consult their doctor; codeine can pass into breast milk.
Do not exceed 4 grams of acetaminophen per day from all sources (including OTC medications).,Avoid alcohol while taking this medication; risk of liver damage increases.,This medication may cause dizziness, drowsiness, or hallucinations; avoid driving or operating machinery until effects are known.,Report any signs of allergic reaction (rash, difficulty breathing) or liver issues (yellow skin/eyes, dark urine).,Do not suddenly stop if used long-term; withdrawal symptoms may occur.,If you have opioid dependence, this medication may precipitate withdrawal symptoms.,This medication may cause constipation; maintain fluid and fiber intake.
"Pirenzepine, a selective M1 muscarinic antagonist, reduces gastrointestinal motility and secretions, while codeine, an opioid agonist, also decreases gastrointestinal motility via mu-opioid receptors. Concurrent use leads to additive anticholinergic and opioid effects, resulting in enhanced risk of severe constipation, paralytic ileus, and central nervous system depression. Clinically, patients may experience exacerbated sedation, respiratory depression, and urinary retention."
"Ropinirole, a non-ergoline dopamine agonist used in Parkinson's disease and restless legs syndrome, may reduce the analgesic efficacy of codeine. This is likely due to pharmacodynamic antagonism at central dopamine and opioid receptors, as well as potential pharmacokinetic interactions that decrease the conversion of codeine to its active metabolite morphine via CYP2D6 inhibition by ropinirole. The resultant blunted opioid response can lead to inadequate pain control, necessitating dose adjustment or alternative therapy."
"Vemurafenib induces CYP3A4, significantly reducing the plasma concentrations of codeine, which is metabolized via CYP3A4 to its active metabolite morphine. This may diminish codeine's analgesic efficacy, potentially leading to inadequate pain control. Additionally, reduced formation of morphine may lower the risk of opioid-related adverse effects."
"Pentazocine, a mixed opioid agonist-antagonist, may attenuate the central nervous system (CNS) stimulant effects of dextroamphetamine by competitively blocking mu-opioid receptors and potentially altering dopamine release, leading to reduced analgesic efficacy of pentazocine and diminished therapeutic response to dextroamphetamine in treating attention deficit hyperactivity disorder (ADHD) or narcolepsy. This interaction can result in suboptimal pain control and exacerbation of ADHD symptoms, requiring dose adjustments or alternative therapies."
"The concurrent use of ipratropium, an anticholinergic agent, and pentazocine, a mixed opioid agonist-antagonist, may lead to an increased risk of central nervous system (CNS) depression and anticholinergic adverse effects. Pentazocine can enhance the sedative and respiratory depressant effects of ipratropium, while ipratropium may potentiate pentazocine's anticholinergic actions, such as dry mouth, blurred vision, constipation, and urinary retention. Clinically, this interaction can result in excessive sedation, confusion, and impaired cognitive and motor function, particularly in elderly or debilitated patients."
"The combination of pentazocine, a mixed agonist-antagonist opioid, with triazolam, a benzodiazepine, can lead to additive central nervous system (CNS) depression, including increased sedation, respiratory depression, and psychomotor impairment. This is due to the synergistic effects of both drugs on GABAergic and opioid receptors in the brainstem and cortex. Clinically, this may result in excessive drowsiness, confusion, ataxia, and an elevated risk of falls or respiratory compromise, particularly in elderly or debilitated patients."
Explore head-to-head clinical comparisons of other medications in the same therapeutic classes.
Common clinical questions about TYLENOL W/ CODEINE NO. 4 vs ACETAMINOPHEN AND PENTAZOCINE HYDROCHLORIDE, answered by our medical review team.
TYLENOL W/ CODEINE NO. 4 is a Opioid Agonist that works by Codeine is a prodrug that undergoes O-demethylation by CYP2D6 to morphine, which acts as a μ-opioid receptor agonist, inhibiting adenylate cyclase and modulating neurotransmitter release in the CNS. Acetaminophen inhibits cyclooxygenase (COX) enzymes, primarily in the CNS, reducing prostaglandin synthesis and modulating pain perception.. ACETAMINOPHEN AND PENTAZOCINE HYDROCHLORIDE is a Opioid Agonist-Antagonist that works by Pentazocine is a mixed agonist-antagonist opioid analgesic that binds to mu, kappa, and sigma opioid receptors, primarily acting as an agonist at kappa receptors and partial agonist at mu receptors, resulting in analgesic and sedative effects. Acetaminophen (paracetamol) is an analgesic and antipyretic whose mechanism involves inhibition of cyclooxygenase (COX) enzymes, primarily COX-2, in the central nervous system, and possibly activation of descending serotonergic pathways.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between TYLENOL W/ CODEINE NO. 4 and ACETAMINOPHEN AND PENTAZOCINE HYDROCHLORIDE depend on the specific clinical indication. These are agents from distinct pharmacological classes and are not directly interchangeable by dose. A physician or clinical pharmacist should guide any therapeutic switching decisions.
The standard adult dose of TYLENOL W/ CODEINE NO. 4 is: One or 2 tablets (acetaminophen 300 mg-codeine 60 mg per tablet) orally every 4 hours as needed for pain; maximum 12 tablets per day.. The standard adult dose of ACETAMINOPHEN AND PENTAZOCINE HYDROCHLORIDE is: One tablet (acetaminophen 500 mg / pentazocine hydrochloride 25 mg) orally every 4 hours as needed for pain; maximum daily dose: acetaminophen 4000 mg (8 tablets) and pentazocine hydrochloride 200 mg (8 tablets).. Dosing should always be individualized based on indication, renal and hepatic function, age, and other patient factors.
No direct drug-drug interaction has been formally documented between TYLENOL W/ CODEINE NO. 4 and ACETAMINOPHEN AND PENTAZOCINE HYDROCHLORIDE in current clinical databases. However, individual patient risk factors including other medications, organ function, and comorbidities should always be evaluated by a qualified healthcare provider.
The maternal-fetal safety profiles differ. TYLENOL W/ CODEINE NO. 4 is classified as Category D/X. Pregnancy Category C prior to 2015; current data insufficient for definitive risk. Acetaminophen: no consistent evidence of major malformations; codeine: opioid use in first trimes. ACETAMINOPHEN AND PENTAZOCINE HYDROCHLORIDE is classified as Category A/B. Acetaminophen: Generally considered low risk; no consistent evidence of teratogenicity in any trimester. Pentazocine: Limited human data; animal studies show no teratogenicity at c. Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.